The subject invention is directed toward the art of electrical fuse boxes and, more particularly, to an electrical fuse box that attaches directly to the battery of a motor vehicle to ensure that shorts occurring in high current conducting wires are fused near the battery rather than at remote locations such as, for example, under the hood or in vehicle kick panels.
The invention is especially useful in the motor vehicle art and will be described with reference thereto; however, the invention is capable of broader application and could be used in other type vehicles and in many environments such as industrial processes.
It is well known in the motor vehicle art to place fuse boxes in the anterior area of the vehicle such as, for example, under the hood within the engine compartment or behind kick guards in the foot area of the interior of the motor vehicle. The fuse boxes serve to accept electrical fuses for individual electrical load consumers within the vehicle such as individual lights or small equipment items and also to accept electrical fuses for large cable strands carrying large amounts of current branching off from the fuse box for servicing entire load sections within the vehicle. Typical fuse boxes are connected to the positive pole of the motor vehicle battery via one or more cables leading to the fuse box whereat power is supplied to a plurality of fuses contained within the box. The ends of the fuses opposite the end connected to the positive terminal of the battery generally are connected to outgoing cables or cable strands to supply power to electrical consumers such as, for example, motor vehicle lighting systems, sensors and switches, and power accessories.
With regard to fuse protecting the smaller general electrical consumers within the motor vehicle, each of the electrical consumers is simply connected to the outgoing end of a respective fuse. In that way, if a short occurs in the power consumer end, the fuse simply melts at a designated melting zone thereby opening the electric circuit and disconnecting the power consumer from the battery downstream of the fuse box. However, when the fuse box is employed to serve and electrically protect entire cable strands that are typically used to serve a large number of electrical connectors, a plurality of smaller sized fuses are generally employed downstream of the large cable from the fuse box so that each of the individual power consumer circuits branching off from the main cable strand can be fuse protected.
For the protection of large cable strands carrying high amounts of current, large fuses are used. They are commonly referred to in the industry as xe2x80x9cstrip fusesxe2x80x9d. The so-called strip fuses generally have no housing of their own and are typically employed to fuse protect cable strands that are expected to conduct high amounts or levels of electrical current. In contrast to the readily manually installable flat fuses which are commonly used to electrically fuse protect individual power circuits in the motor vehicle, the replacement of the strip fuses are usually performed only by skilled personnel since the destruction of strip fuses serving entire cable strands is usually an indication of a serious fault in the electrical wiring of the motor vehicle. Serious faults of this type usually result in excess current intensities and consequently melt a fusible area formed in the respective strip fuse.
On the other hand, the replacement of ordinary insertable flat fuses used to fuse protect individual electric consumer circuits in the motor vehicle is typically within the capabilities of untrained personnel such as, for example, motor vehicle operators or owners. Manufacturers of motor vehicles entrust operators to perform insertable flat fuse replacement because their failure is usually caused only by minor electrical faults such as, for example, a short-circuit occurring in the filament of an electrical bulb when it fails.
One major disadvantage of typical fuse boxes used in the past is made evident during a motor vehicle accidents, in particular, during collisions. In that regard, during certain motor vehicle crashes that result in a mechanical destruction of the electrical cable strands extending between the fuse box and the vehicle battery, short circuits can be produced between the end of the destroyed electrical cable strand and the motor vehicle frame or other vehicle component connected to ground. The severed end of the electrical cable strand of course continues to be connected to one pole of the motor vehicle battery on one end and directly to the body or frame of the motor vehicle on the other or destroyed end. Of course, the motor vehicle body or frame is typically connected to the oppositely polarized terminal of the motor vehicle battery creating a dead short having high current carrying capacity. In such event, sparks are typically generated sometimes causing motor vehicle fires and explosions.
There is a need, therefore, to provide a fuse box for use with motor vehicles which will safely prevent short circuits and the hazards caused thereby even during motor vehicle crashes. It is further desired that such a fuse box can be produced in a simple and cost effective manner and can be easily installed in a wide range of motor vehicles and other electromechanical devices.
In accordance with the subject invention, an electrical fuse box for use in motor vehicles is provided having a housing adapted at a first location to receive an associated electrical strip fuse for protecting a high current conducting wire strand. The strip fuse has a melting zone formed therein designed to melt and open a circuit conducting current that reaches a level beyond a predetermined threshold. The electrical fuse box includes at least one screening zone formed by the housing. The screening zone defines an area located relative to the first location of the strip fuse for collecting liquid melted material generated when the strip fuse melts. In that way, melted material is contained within the screening zone to prevent damage to the other circuits disposed in the fuse box. The melted fuse material is thereby prevented from migrating into other areas of the housing.
Preferably, the fuse box is connected directly to one terminal of the motor vehicle battery to ensure that there are no xe2x80x9clivexe2x80x9d wires, i.e. wires connected to a source of power, extending between the battery and the fuse box. In the event of a crash of the vehicle or destruction to the fuse box, all of the current conducting wires routed through the vehicle are protected by fuses that are connected on one end directly to the battery.
In accordance with the invention, the fuse box is arranged for direct connection to the battery of the motor vehicle. In that way, reasonable assurance is provided that, in the event of a vehicle crash, there will be no destruction of cable strands not protected by a fuse. In that way, the formation of sparks caused by the short circuiting of unprotected cable strands is unlikely or impossible.
In accordance with another aspect of the invention, the fuses used to electrically protect cable strands carrying large amounts of current are preferably strip fuses which are inexpensive and generally readily available.
In the preferred embodiment of the invention, the fuse box is adapted to connect one end of several strip fuses directly to an electrical pole of the motor vehicle battery through a common busbar.
In accordance with yet another aspect of the invention, first ends of the multiple strip fuses contained within the fuse box are connected to the common busbar using screws and nuts to provide minimal connection transition resistance between the fuses and the battery. Bushings are also arranged between the fuses and the terminal elements within the fuse box. This arrangement results in the benefit of a very simple mechanical construction and thus realizes a cost effective fuse box that is readily and inexpensively produced.
In accordance with the preferred embodiment of the invention, each strip fuse includes a pair of drill holes which adapt the fuse ends for attachment by means of a threaded bolt and nut. The end of the strip fuse which contacts the common busbar is placed upon a threaded bolt which protrudes via a bore hole into the common busbar and is securely fixed to the busbar by means of a nut threaded onto the bolt. A spring plate is preferably inserted between the fuse and the nut. The spring plate serves to maintain a predetermined starting torque for the nut so that the nut does not vibrate loose from the bolt. A lock washer could equivalently be used in place of the spring plate.
The spring plate and mechanical nut and bolt attachment of the fuse is particularly advantageous when the strip fuse is made of zinc. It has been shown that during the course of time the staring torque for removing the nut is reduced as a result of a setting property of the zinc material, particularly under the effect of temperature cycles upon the connection between the busbar and the strip fuse.
In accordance with another preferred aspect of the invention, lateral contact surfaces are provided in the fuse housing for providing torsional protection to the installed strip fuses. The torsional protection results in the advantage that twisting or deformation of the fuse is avoided or prevented during the tightening of the nut onto the bolt head as the fuse is attached in place.
In addition, in the preferred embodiment of the invention, the housing is formed in a manner that the fusible areas of the strip fuses are each individually isolated from each other and from other fuses by a set of screening zones provided in the housing. The screening zones provided for each individual strip fuse results in the advantage that as the fusible area of the fuse blows and is melted, the melted material is contained within the screening zone in both liquid and then frozen states, and is thereby prevented from migrating into unsuitable or undesirable areas within the housing. In prior fuse boxes, no such screening zone was provided and, accordingly, melted material oftentimes migrated into undesirable areas within the housing having deleterious effects on other electrical circuits within the housing.
In accordance with yet another aspect of the invention, the screening zones provided for each individual strip fuse in the subject fuse box also functions to provide mechanical coding with respect to the current carrying capacity of the strip fuse to be installed at each individual screening zone location. In this manner, it is possible to avoid installing fuses with higher rated current carrying capacity in the fuse locations designed for lower rated currents. Conversely, the mechanical coding feature provided by each individual screening zone ensures that fuses with lower rated current carrying capacities do not physically fit into in connection locations where strip fuses having higher current capacities are needed. Generally, strip fuses having higher rated current carrying capacity, while having identical thickness to lower rated fuses, have broader melting zones than fuses with lower rated currents.
In a similar fashion, the regions of the housing adapted to accept cable terminal ends are preferably formed in such a manner to achieve a mechanical coding based on the physical size of the conductors and terminal ends. To that end, it is anticipated that there is a difference in the geometric shape of the individual current carrying cable terminals at the ends of the cables that are connected to the fuse box. The housing is shaped to prevent a mismatch between the terminals and the desired terminal locations. In this manner, accidental erroneous installation of the cable terminals into the fuse box is avoided so that cable terminal ends are not connected to fuse locations where they are not intended to be placed.
In addition to the coding measures of the housing described above, it is a further aspect of the invention to provide the lateral openings used for leading the respective cables into and out of the fuse box with openings sized essentially to correspond with the outer diameter of the respective cables expected to extend therethrough. Since cables for conducting higher currents are generally thicker than cables intended to conduct lower currents, the multiple varied opening sizes of the cable entrance ports further prevents installation of cables intended for higher currents at fuse locations intended to serve lower current circuits. Conversely, the multiple varied entry port sizes make the installation of thinner cables for lower currents at fuse locations for higher currents immediately evident because, in that case, the cable is not tightly sealed off by the housing cable entrance port nor is it securely retained in the housing side wall. Rather, the small cable is only loosely held in the opening.
Preferably, in accordance with the fuse box of the present invention, the contact surfaces of the housing providing torsional protection for the strip fuses, the screening areas providing melt zones for the fuses, the fuse coding areas, and the cable terminal coding areas are all formed in intermediary bottom members which are adapted to be selectively installed within the fuse box housing. A set of intermediary bottom members having different size combinations of the above features enables the fuse box to be adapted to accommodate different fuse values and different quantities of fuses. Also, the intermediary bottom member enables captively retaining the threaded bolts in the housing so that the thread zones of the threaded bolts project through bore holes into the intermediary bottom member. The headpieces of the threadbolts are held between the housing bottom and the underside of the intermediary bottom member.
In the preferred embodiment of the subject fuse box, each of the threaded bolts used to fasten the strip fuse ends protrude through a captive spring bushing which is retained in the housing, preferably pressed in. When the intermediary bottom member is employed, the spring bushing may be pressed into a bore hole provided therein. The spring bushing has, in this arrangement, a bushing region extending generally axially relative to the threaded portion of the threaded bolt. The bushing region is adapted to be pressed into the intermediary bottom member. The spring bushing also includes a radially extending collar for resilient placement of the strip fuse thereon. The radially extending collar ensures, by means of its resilient property, that the initial starting torque of the nut is maintained when fastening the respective cable terminal at the threaded bolt or the respective fuse end.
By providing captively retained threaded bolts and spring bushings in the housing, the fuse box can be supplied by the manufacturer of the fuse box with preinstalled strip fuses. The preinstalled strip fuses and captively retained threaded bolts and spring bushings make it possible, when installing the fuse box in a motor vehicle, to merely attach the fuse box onto the battery and then connect the cable terminals to the respective free ends of the strip fuses.
In the preferred embodiment of the fuse box according to the invention, the housing member comprises a cover member which is connectable to the remaining portion of the housing in a water proof and moisture proof manner. In this arrangement, a housing member lid is connectable with a remaining or bottom portion of the housing by means of a snap mechanism, suitable hinges, screws, or the like. This results in the benefit that when the lid is opened, all of the fuses are easily accessible. Conversely, when the lid is closed, the fuses and the circuitry contained within the fuse box are protected from environmental influences. Thus, individual protective caps or other sealing arrangements for the strip fuses are not needed. As can be seen from the foregoing, a primary object of the invention is to provide a fuse box that is directly connectable to a motor vehicle battery terminal.
A further object of the invention is the provision of a fuse box having multiple screening zones formed in the fuse box housing to collect melted material generated from blown fuses so that the melted material is contained within the screening zone to prevent damage to the remaining circuits in the fuse box.
Another object of the invention is the provision of a fuse box that is mechanically coded so that wrong sized fuses cannot be inadvertently inserted into the fuse box where they do not belong.
Yet another object of the invention is the provision of a fuse box that provides mechanical torsional integrity to the strip fuses so that they are not bent or otherwise mechanically damaged as they are installed or connected to the busbar or as their free ends are connected to the electrically serviced circuit.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.